The Vector Core will have two Specific Aims: 1. Design and construct retroviral and lentiviral vectors for gene transfer and expression in hematopoietic stem and progenitor cells and their progeny. 2. Package the vectors into high titer viral preparations. The Vector Core will use current state-of-the-art retroviral, lentiviral and spumaviral vectors and packaging systems to design, construct, package and perform initial characterization of retroviral and lentiviral vectors for investigators of the Projects to pursue their scientific objectives.